1. Field of the Invention
The present disclosure relates to a catalytic converter which is accommodated and fixed in a pipe which is consisted of an exhaust system of exhaust gas.
2. Description of Related Art
In various industries, large effect has been made world widely to reduce the environmental influence load, especially in the automobile industry, not only the gasoline engine automobiles with excellent fuel efficiency, but also the popularization of so-called eco-cars such as hybrid automobiles and electric automobiles and the improvement of their performances are developing every day. Besides the development of such eco-cars, research about the exhaust gas purification catalyst for purifying the exhaust gas exhausted from the engine is also extensively conducted. The exhaust gas purification catalyst includes oxide catalyst, three-way catalyst, NOx storage reduction catalyst, etc.; in the exhaust gas purification catalyst, noble metal catalyst, such as Platinum (Pt), Palladium (Pd), Radium (Rh), etc., is found to have catalyst activity, and the noble metal catalyst is usually used under a state supported by a support consisted of porous oxide such as alumina.
The gas exhaust system that connects the automobile engine and muffler is usually provided with a catalytic converter for purifying the exhaust gas. Sometimes, engine would emit environmental harmful substances such as CO, NOx, or uncombusted HC and VOC, in order to convert such harmful substances to acceptable substances, the exhaust gas passes through the catalytic converter, so that CO is converted to CO2, NOx is converted to N2 and O2, and VOC is combusted and generates CO2 and H2O, and the catalytic converter is provided by disposing a catalyst layer, in which the noble metal catalyst, such as Rh, Pd, and Pt, is supported by a support, on a cell wall of a substrate.
Incidentally, as an embodiment of the catalytic converter of related art, a tandem catalytic converter provided by disposing two cell structured substrates along a flowing direction of the exhaust gas may be used. The tandem catalytic converter changes the types of the noble metal catalyst and supporting amount supported at the substrate a the upstream side and the substrate of the downstream side, so as to achieve high catalyst activity.
Herein, FIG. 7 illustrates a catalytic converter in which two substrates are mounted in tandem of related arts. As illustrated in FIG. 7, the catalytic converter is as follows: at each of the upstream side (front side, Fr side) and downstream side (rear side, Rr side) of the flow of the exhaust gas in the interior of the duct H that consists the pipe system, is provided with one cell structured substrate, with a total of 2 cell structured substrates K1, K2, a catalyst layer consisted of the support and noble metal catalyst supported by the support are formed on the cell walls of the of the substrates K1, K2. In the catalytic converter, the cell densities of normal substrates K1, K2 are uniform.
Incidentally, since gas flow normally flows in the substrate with a relatively high flow rate at the center portion of the duct (center portion of the substrate) where there is no friction influence with the wall of the duct H, the problem is that in the cell structured substrate illustrated in FIG. 7, the flow rate distribution of the exhaust gas at the center area of the cross section of substrates K1, K2 is higher compared with that of the surrounding area, resulting in a reduction of exhaust gas amount flowed in the surrounding area, thus the catalyst in such area cannot be sufficiently used, and as a result, catalyst of the whole substrate cannot be sufficiently used.
As for the above problem, to improve the configuration of the tandem catalytic converter illustrated in FIG. 7 of related art, Japanese Patent Application Publication No. 9-317454A (JP 9-317454 A) discloses a catalytic converter as follows: changing the cell densities of the substrate at the upstream side and the substrate at the downstream side of the gas flow at the center area and surrounding area respectively, thereby equalizing the flow rate distribution and temperature distribution of the whole catalytic converter.
The catalytic converter disclosed in JP 9-317454 A is simulated in FIG. 8. In the catalytic converter illustrated by FIG. 8, in the substrate K1 at the upstream side, a center area K1a has a relatively higher cell density compared with that of a surrounding area K1b; and in the substrate K2 at the downstream side, in contrast, a surrounding area K2b has a relatively higher cell density compared with that of a center area K2a.
In the catalytic converter having substrates K1, K2 with such cell densities, after the exhaust gas flows along a direction X1 while entering the catalytic converter, in substrate K1 at the upstream side, the exhaust gas mainly flows in the surrounding area K1b where the cell density is low and the gas easily flows (direction X1′), then in the substrate K2 at the downstream side, the exhaust gas flows mainly in the center area K2a where the cell density is low and the gas easily flows.
However, as illustrated by FIG. 8, under a state that the cell density of the center area K1a of the substrate K1 at the upstream side where the exhaust gas initially flows with respect to the catalytic converter is high, the pressure loss to the exhaust gas flowing into the center area K1a with high flow rate distribution is high, as a result, the flow of the exhaust gas towards the substrate K1 is impended, thus the inflow amount of the exhaust gas to the catalytic converter is reduced.
Furthermore, if the inflow amount of the exhaust gas to the catalytic converter is reduced, the heat supply to the catalytic converter is inevitably reduced, and the warming-up performance after the starting of the engine is reduced. Along with the reduction of the warming-up performance after the starting of the engine, the emission (cold emission) of the HC and NOx is reduced.
In addition, Japanese Patent Application Publication No. 2000-97019 A (JP 2000-97019 A) discloses a catalytic converter (herein is an exhaust gas processing device for an automobile) provided with a substrate with a high cell density of a center area at the upstream side, and a substrate with uniform cell density at the downstream side.
However, even according to the catalytic converter disclosed by JP 2000-97019 A, it is the same with that disclosed by JP 9-317454 A, since the cell density of the center area of the substrate at the upstream side is high, the problem that the exhaust gas flow is impended and the inflow amount of exhaust gas is reduced still exists.